The present invention relates to a method of manufacturing a composite microwave circuit module and, more particularly, to a method of manufacturing a composite microwave circuit module comprising a multilayer dielectric substrate suitable for high-frequency signal line/waveguide conversion.
Elements of a conventional composite microwave circuit module are shown in either one or both of FIGS. 4 and 5. In the composite microwave circuit module, an upper-surface ground 3 and a lower-surface ground 4 (FIG. 5) are formed on the upper and lower surfaces of a multilayer dielectric substrate 1 (FIG. 4), respectively, and a high-frequency signal line 8 (FIG. 5) for transmitting a signal is formed on a high-frequency signal layer 23 (FIG. 5) as an interlayer. Shield via holes 2 (FIG. 5) filled with a conductive material such as silver or copper are formed to electrically connect the upper-surface ground 3 to the lower-surface ground 4 and provide a shield effect. A cavity 11 (FIG. 5) is formed by removing a portion from the surface to the high-frequency signal layer 23 (FIG. 5), in which an active element 20 and a passive element 21 (FIG. 4) are mounted. After these elements are mounted, and electrical adjustment is completed, the cavity 11 is sealed with a metal cap 12, thereby protecting the elements from dust and humidity and electrically shielding the elements.
The high-frequency signal line 8 is realized by a strip line, a microstrip line, a coplanar line, or the like.
In FIG. 4, pseudo waveguides are shown as 6 and 7, and an antenna pattern as 10. In FIG. 5, a voltage pattern or power supply pattern is shown as 22, and bonding wires as 13.
FIGS. 3A and 3B show the waveguide connection structure of such a composite microwave circuit module consisting of a multilayer dielectric substrate, in which a waveguide is used to connect the high-frequency signal layer. Elements of the waveguide connection are shown in either one or both of FIGS. 3A and 3B.
An antenna pattern 10 is formed by the high-frequency signal line 8 on the interlayer, and an adjustment pattern 14 (FIG. 3B) is formed around the antenna pattern 10. The lower layer has a cavity structure. The antenna pattern 10 and the adjustment pattern 14 are connected by bonding wires 13 (FIG. 3B), thereby performing electrical adjustment. FIG. 3A shows the cavity 11 sealed with the metal cap 12 after electrical adjustment.
The cavity 11 is surrounded by the shield via holes 2 connected to the upper-surface ground 3 and the lower-surface ground 4 (FIG. 3A) to provide the shield effect. This structure functions as a pseudo waveguide in the substrate. An opening 15 having the same shape as the sectional shape of the waveguide is formed in the upper-surface ground 3. A waveguide 5 (FIGS. 3A and 4) is electrically connected to the opening 15 through a metal shim 19 (FIGS. 3A and 4).
Some radio waves radiated from the antenna pattern 10 are transmitted through the upper ceramic substrate 1 and reach the waveguide 5, and the remainings are transmitted through the lower cavity 11, reflected by the metal cap 12, and then reach the waveguide 5. The depth of the cavity 11 is set at 1/4 the wavelength of the frequency in use. The radio waves reflected by the metal cap 12 return to the antenna pattern 10, where these radio waves and those transmitted to the upper layer are in phase and intensify each other.
This is the waveguide connection structure of a microwave circuit module.
In the above-described conventional waveguide connection structure of a microwave circuit module, however, the degree of freedom of design for matching impedances between the waveguide and the layers above and below the antenna pattern in the substrate is low, so substantially no impedance matching design is available. In addition, in the pseudo waveguide, radio waves are attenuated due to a dielectric loss caused by the ceramic material, i.e., the dielectric substrate.